Circuit interrupter



Patented May 26, 1953 CIRCUIT INTERR UPTER Harold H. Fahnoc, Wilkinsburg, and William J.

Paxton, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation, of Pennsylvania Application May 2, 1952 Serial'No. 285,694

( zoos-v.0)

'7' Claims. 1i

This invention relatesto an improvement on high voltage circuit interrupters, particularly of the type described and claimed in the patent of :Hrh-Rawlins, ct al serial No. -2, l0-3,121, granted Ju1y;2, l946:

Circuit interrupting, devices of this type are subjected inservlc e in power-line circuits to voltages high enou h to make corona a problem. Corona itselfis not harmful, however, there are serious secondary effects which result from the production of' powerful oxidizing agents in an intense electrical field. Ozone is produced, which accelerates oxidation of adjacent organic materials. Nitrogen oxide components, produced by the ionization of-the air, combine with water to form acids that attach the internal metallic parts of the circuit interrupter unit.

Serious difficulties have been experienced by reason or the accumulation of incr-ustations of nitrous salts on the above-mentioned internal metallic parts, by reason of the reaction of the inetal,general;ly copper, with the acids formed by "the corona. "Ijhese incrustations are deposited during the period of time when the device is carrying line current, that is, before it undertakes to perform its circuit interrupting action in re sponse to an overcurren-t in the line.

' This difficulty has been a problem, particularit is necessary for an arcing contact rod to be withdrawn longitudinally through the bore of a gas-evolving liner, such as boric acid, during-the circuit interrupting operation of the fuse. The bore of this boric acidlinermust be as small as practicable, in order that the arc which results from the current interruption will come into contact with the side walls of saidbore, as the rod is being withdrawn out of-thebore during the circult interrupting operation. This contacting of the liner by the arc is necessary so that the surfaces of said bore will evolve arc-extinguishing gases. In order that-the rod shall have sufilcient mechanical strengthand currentcarrying ability, the outer diameter of the rod is made as large as is permitted by the diameter of the bore of theboric acid linenand with the minimum possible clearance, so that it does not take very 'much outer incrustation on the rodto prevent it from being withdrawn through'the bore of the boric acid liner during the circuit interrupting operation.

:In an'attempt-to'solve this corrosion problem,

the internal metallic parts of a fuse unit were plated with .many .metallic coatings, including 2. silver, cadmium, zinc, gold, etc. These applied metallic coatings, however, were soon tarnished and corroded when subjected to corona conditions.

.To thebest of our knowledge, it has never, heretofore, beentaught nor suggested how tosuccessfully prevent the detrimentalefiecl's of corona in high voltageelectrical fuses by providing a pro tectivecoating on the internal metallicparts.

An object of this invention is thus to provide protection 'for the internal metallic parts of a high. voltage circuit interrupter unit'from the formation of corrosion deposits and incrustations thereon caused by corona by applying a silicone coatin to theparts afiected.

Other objects of: the invention will, in part, be obvious, and will, in. part, appear hereinafter.

For a fuller understanding of the nature and objects of the inventionreference should be had tov thefollowing detailed description and drawing,inwhich:

Figure 1 is a schematic vertical longitudinal sectional view showing aniexemplary circuit interrupter assembly embodying our invention, and

Fig. ;2 is a sectional View. taken on the line 'IIfiI'I of Fig. 1.

We have discovered that the detrimental efi ects, of corona on the internal metallic parts in a circuitinterrupter unit areprevented'by applying to the parts affected a silicone coating. The metallic-parts affected are generally those. having a, relatively small crossrsectional area, particularly the. arcing contact rod, fusible interrupter strips, and sliding contacts. Either of two types of Silicone coatings are applied, the particular one selected depending upon the function of the metallic part tobe coated. A coating of hardened silicone varnish is applied to the arcing contact rodand interrupter strips and a coating of silicone fluid is applied to the sliding contacts for reasons to behereinafter described. All of the part subject. to. Corona, however, may becoated with silicone fluid, or if desired, a coating of silicone fluid, to act as a lubricant, may be applied over the silicone varnishcoating.

In practicing ourinvention. wefirst silver plate all the metalli parts tobc treated. The silverplateis not essential, however, it provides a better silicone to metal bond. Other metalplating may he used, such as cadmium or zinc. Two coatings of silicone varnish are applied over the silver plate on the parts, such as the arcing rod, not subject to sliding contact. Each coating of the Silicone varnish is baked after being applied. The-baked silicone varnish forms a hard glazed surface which is not affected by the heat generated inside the interrupter unit. This permits free withdrawal of the arcing rod when a circuit interruption occurs. The silicone fluid applied to the electrically conducting parts having sliding contact will remain in a fluid state after application in order that a metal to metal electrical contact is maintained during sliding movement of the contacts. The fluid surrounds the contact, flowing to cover any area exposed during movement, and thus in this manner the metal is always protected.

Silicone varnishes for use in the practice of this invention may comprise a silicone resin dissolved in a suitable solvent. The silicone resins are thermosettable polymers containing an R, to Si ratio of from 1.1 to 2. The R represents monovalent organic groups and may comprise monovalent alkyl groups such as methyl, ethyl, and propyl, aryl groups such as phenyl, tolyl and xylyl, and alkaryl groups such as benzyl. The silicone resin may comprise a single type of R. groupsfor example a polymethylsiloxane having an R to Si ratio of 1.4--or different groupsfor example a phenylmethyl polysiloxane having an R to Si ratio of 1.5 and a substantially equal number of phenyl to methyl radicals. Suitable solvents are toluene and xylene. The phenyl methylene siloxane above mentioned forms a suitable varnish when dissolved in 3 parts by weight of toluene for each part of resin.

The silicone fluids are liquid organo-silicon oxide polymers either linear or cyclic in molecular structure and often comprise both linear and cyclic polymeric units. The silicon atoms of the organo-silicon oxide polymers are joined to other silicon atoms through an oxygen linkage, namely Si-OSi, and all valences of the silicon atoms not taken up by such oxygen linkages are satisfied by monovalent organic radicals attached to the silicon atoms through a carbon to silicon bond (except for possibly a few residual OH or other groups attached to silicon). The organic radicals are saturated alkyl radicals such as methyl, ethyl, propyl, isopropyl, butyl, aryl, hexyl and higher. Saturated alicyclic radicals such as cyclohexyl and methyl cyclohexyl; aryl and saturated alkaryl radicals such as phenyl, benzyl, tolyl, naphthyl xylyl and mesityl may be attached to a small proportion of the silicon atoms. The preferred fluids are dimethyl silicones.

Illustrated in Fig. 1 of the drawing is an exemplary form of circuit interrupter embodying the invention. The circuit interrupter unit is constructed of a fuse tube of insulating material, such as fiber, synthetic resin or the like, and opposite ends of the fuse tube are closed by end terminal caps 4, 6 respectively, fastened thereto by cooperating indentations. Within the lower portion of fuse tube 2, as viewed in Fig. l, are a plurality of blocks 8, of an insulating material which is capable of evolving an arc extinguishing gas when in proximity to an electric arc. The insulating material 8 is preferably boric acid, but any other insulating material having the property set forth above may be employed, such, for example, as horn fiber or a synthetic resin as urea-aldehyde polymer. The insulating blocks 8 are each provided with a central bore I0, so that the bores, when the blocks are mounted in the tube 2, form an elongated arc passage of restricted cross-section. The lower end of the arc passage formed by bores 10 is outwardly flared portion [2. Disposed on end cap 6 is a lower block [4 which supports the blocks 8 in position.

Cii

The block 14. is preferably of the fiber or a synthetic resin which has a greater mechanical strength than boric acid.

An arcing contact rod I6 is adapted to be normally positioned within the arc passage formed by bores It]. The lower end of rod I6 is electrically connected to the terminal cap 6 by a fusible strip l8, paralleled by a strain member 20, secured in any desired manner to the rod [6 and terminal cap 6. As shown, fusible strip l8 and strain member 20 have one end inserted in a slot in the lower end of arcing contact rod I6 to be secured therein, as by soldering or riveting, and the other end of the fuse strip and strain means is bolted or otherwise secured as by the screw 24 to an inwardly bent tongue 22 formed integral with end terminal cap 5. Fusible strip I8 may be of any desired fusible material, such, for example, as silver, zinc, tin, or alloys thereof. The strain member 20 paralleling the fusible strip is preferably of a higher resistance material which has a greater tensile strength than the material comprising fusible strip 18.

A conducting washer 28 is mounted within fuse tube 2 immediately above insulating-blocks 8. Abutting on washer 28 is a tube 30 of good electrical conducting material, the latter being clamped between end terminal cap 4 and the upper end of fuse tube 2. As shown in Fig. 1, an end washer 32 is provided with a central aperture and with integral inwardly extending supporting and looking tongues 34, for a purpose to be hereinafter referred to. Just above the conducting washer 28, arcing contact rod I6 is provided with an enlarged portion 36 having a tapered lower surface 38, on which is seated an end coil 44 of a coiled tension spring 40. The opposite end coil of spring 40 is upported by tongues 34'. The rod 16 is biased upwardly towards end terminal cap 4 by spring 40 and strain member 20 is normally maintained under tension thereby.

In order to provide a good electrical connection from arcing contact rod Hi to terminal cap 4, flexible strips 42 of a conducting material such as copper, are preferably secured to conducting washer 28 at the lower end of conducting tube 30, and the free ends of the strips are inserted between the tapering contact surface 38 on the arcing contact rod and the lower coil 44 of spring 40. Thus, spring 40 also acts to maintain contact strips 42 in engagement with the tapered surface 38 on the contact rod under pressure.

The contact strips 42 and end coil 44 are in sliding contact with the tapered surface 38 of the enlarged portion 36 in order to allow for expansion and contraction resulting from changing temperatures incurred during operation of the device. Also, the enlarged portion 36 must be freely disengageable from the contact fingers 42, in response to fusion of fusible strip 18 and strain member 20 upon the occurrence of an overload of current through the circuit.

It will be noted that arcing contact rod I6 is provided with an integral extension 46 above enlarged portion 36, and that the end terminal caps 4 and 6 are each provided with a central aperture normally closed by displaceable closure disks 48 and 50, respectively, which may be releasably maintained in position, such, for example, as by cementing or the like.

The electric circuit through the fuse described above extends from one end terminal cap 4 through conducting washer 32, conducting tube 30, contact strips 42, contact arcing rod l6, fusible amen-es strip 18 :to the :other end terminal cap 6. When an overload occurs on the circuit in which the .fuse'isconnecte'd, fusible strip It will melt and strain member will be vaporized shortlythereafter, to thereby release arcing contactrod "t6 and permit spring 40 to move .it upwardly towards terminal can 4. ,As soon as fusible strip 1 8 and strainmember 20 are melted, the pressure created in theilare'dpassage IZ, augmentedjby gas evolved from the material of bores [0, as

.arcing rod [,6 .moves upwardly. will .be sufficient to displace. closure disk v5i] to thereby permit the gases to be expelled to theatmosphere. Spring 40 will be effective to move contact arcing rod [6 upwardly and-extension. of the rod will engage closuredisk 48 and displace the disk so that the extension will be projected from terminal cap 4 an amount limited only by engagement of enlarged portion 36 of the rod with tongues 34 on washer 32. It will be noted that the space between tongues 34 is slightly less than the diameter of rod extension 46, so that in passing upwardly between the tongues the extension will bend them upwardly, and the tongues will therefore lock extension 46 in its projecting position and prevent any subsequent tendency of the rod or extension 66 to move into the fuse tube. During interruption, when an arc is drawn between the lower end of arcing contact rod l5 and arcing tongue 22 on end cap 6, contact strips 42 will move out from between the lower turn of spring 40 and the tapered surface 38 on the contact rod, so that as the rod moves upwardly, the current will be carried by spring 40. Inasmuch as the arcing time is very short, it has been found that the spring will be undamaged by the passage of current therethrough for such short periods of time. Coil spring Ml also performs the function of moving contact rod is an amount suiiicient to project extension 46 thereof out through the aperture in terminal cap 4 where it is locked against movement by locking tongues 34.

As shown in Fig. 2 of the drawing, baked coatings of silicone varnish 52 are applied to the arcing contact rod l6, fusible strip l8, and strain member 30 in the manner described at the beginning of the specification. The baked silicone varnish assures the free withdrawal of arcing rod l6 through bore [0 which is of greatest importance in the satisfactory operation of the circuit interrupter unit.

It is also desirable to coat all other of the internal metallic parts of the unit affected, including the enlarged portion 38 and contact fingers 42 in order that there be no corrosion of these parts. The enlarged portion 36 and the contact fingers 42, to be hereinafter referred to as sliding contact means, are painted with a coating of a silicone fluid, silicone varnish not being suitable as hereinbefore described.

Circuit interrupters of the type shown, with a silicone coating applied to the internal metallic parts in accordance with our invention, have undergone tests at voltages in excess of 69 kv. Examination of the interrupters after a considerable period of time showed that they had remained free of corrosion deposits. A circuit interrupter of the same construction, but without the benefit of the protective coatings of silicone as taught by our invention, and operating under the same conditions developed corrosion deposits after several hours service.

The application of silicone varnish and silicone fluid to the internal metallic parts of the interrupter unit affected by corona does not in any way affect the ,operating characteristics e: the

unit. A continuous protective"coating is provided for all metal parts adverselyaffected bycorona. Hence, "the arcing contact -rod t6 does not build upin any area to such an oversized diameter thatit cannot slide freelythrough'the bore l0 of-the gas-evolvingmemberw. "It-isnecessary for only a relatively-small "clearance to 'be provided between the arcing rod Hi and the-bore H], ,because at least "a portion of-thisbore has to be :assmallas possible, in order to best perform its gas evolving function whenplayed upon by an el ctric; arc.

While our invention 1 is primarily designed and aldapteidifor a circuit interrupter of the type described, it "wlllgbe understood'that our invention is not altogether limited .to this particular 1 type of circuit interrupter, as our invention maybe applied to fuses of different construction. Accordingly, it is intended that all material contained in the above description or taken in connection with the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. In a circuit interrupter adapted for service in a circuit at a voltage high enough to form corona, in combination, a tubular enclosure of insulating material having terminals adjacent opposite ends thereof, said terminals being electrically connected by conducting means disposed Within said enclosure, said conducting means including fusible interrupting means capable of automatically interrupting the circuit in response to predetermined electrical conditions, a filler within the tube comprising a solid insulating material which is capable of evolving an arcextinguishing gas when in proximity with an electric are, a restricted bore through said filler,

movable arcing contact rod in said bore normally held against movement by said interrupting means, biasing means for moving the arcing contact through the bore in response to operation of the interrupting means, and a coating of silicone varnish applied to at least the arcing contact rod, and interrupting means to prevent formation thereon of detrimental corrosion deposits caused by corona.

2. In a circuit interrupter adapted for service in a circuit at a voltage high enough to form corona, in combination, a tubular enclosure of insulating material having terminals adjacent opposite ends thereof, said terminals being electrically connected by conducting means, disposed within said enclosure, said conducting means including sliding contact means and fusible interrupting means capable of automatically interrupting the circuit in response to predetermined electrical conditions, a filler within the tube comprising a solid insulating material which is capable of evolving an arc-extinguishing gas when in proximity with an electric are, a restricted bore through said filler, a movable arcing contact rod in said bore normally held against movement by said interrupting means, biasing means for moving the arcing contact through the bore in response to operation of the interrupting means, a coating of a silicone fluid applied to the sliding contact means, and a coating of silicone varnish applied to the interrupting means and arcing contact rod, thereby preventing the detrimental effect of corona thereon.

3. The combination of claim 2 in which the coating of silicone fluid and silicone varnish is applied over a silver plate.

4. The combination of claim 2 in which the coating of silicone fluid and silicone varnish is applied over a cadmium plate.

5. The combination of claim 2 in which the coating of a silicone fluid and silicone varnish is applied over a zinc plate.

6. The combination of claim 2 in which a coating of silicone fluid is applied over the coating of silicone varnish.

'7. In a circuit interrupter adapted for service in a circuit at a voltage high enough to form corona, in combination, a tubular enclosure of insulating material having terminals adjacent opposite ends thereof, said terminals being electrically connected by conducting means, disposed within said enclosure, said conducting means including sliding contact means and fusible interrupting means capable of automatically interrupting the circuit in response to predetermined electrical conditions, a filler within the tube comprising a solid insulating material which is capable of evolving an arc-extinguishing gas when in proximity with an electric arc, a restricted bore through said filler, a movable arcing contact rod in said bore normally held against movement by said interrupting means, biasing means for moving the arcing contact through the bore in response to operation of the interrupting means, a coating of a silicone fluid applied to the sliding contact means, interrupting means and arcing contact rod, thereby preventing the detrimental effect of corona thereon.

HAROLD H. FAHNOE. WILLIAM J. PAXTON.

No references cited. 

